BACKGROUND AND INTRODUCTION Zika virus (ZIKV) is an arbovirus (vector-borne virus) of the genus Flaviviridae. Until recently, infections with ZIKV were thought to be mild and self-limiting. Since 2015 however, ZIKV infections have been associated with an increase in microcephaly and other birth defects in newborns following infection of the mother during pregnancy. More recently, it has been associated with Guillain-Barr Syndrome (GBS) in adults of both sexes. Increasing evidence points to ZIKV as the agent responsible for a variety of birth defects in newborns of mothers who become infected during pregnancy. However, the strength of the causal relationship of ZIKV infections in pregnancies with adverse outcomes of pregnancy has yet to be determined. Most studies to date have followed women known to be infected or infants who were born with serious birth defects. A prospective study of pregnant woman for maternal health in ZIKV-endemic areas is necessary to assess key knowledge gaps about the incidence, causality, and consequence of ZIKV infection in pregnant women on newborn outcomes increasing evidence points to ZIKV as the agent responsible for a variety of birth defects in newborns of mothers who become infected during pregnancy. However, the strength of the causal relationship of ZIKV infections in pregnancies with adverse outcomes of pregnancy has yet to be determined. Most studies to date have followed women known to be infected or infants who were born with serious birth defects. A prospective study of pregnant woman in ZIKV-endemic areas is necessary to assess key knowledge gaps about the incidence, causality, and consequence of ZIKV infection in pregnant women on newborn outcomes. NIH accordingly in 2016 initiated a large, multicenter, international observational study of the epidemiology, natural history, and pathogenesis of Zika in infants and pregnancy. This task order addresses NIH?s requirement to maintain ongoing conduct of the study and complete it successfully. SCOPE The overall objective of this multisite, international ZIP study is to assess the strength of the association between Zika virus infection (ZIKV) during pregnancy and adverse maternal/fetal outcomes or maternal health and the risk of vertical transmission.